A common industrial gas turbine engine configuration utilizes multiple combustors in a circular array about the engine shaft in a “can annular” configuration. A respective array of transition ducts connects the outflow of each combustor to the turbine inlet. Each combustor has an air inlet, followed by a fuel injection assembly, followed by a combustion chamber enclosed by a tubular liner, which is often of double-wall construction. The aft or downstream end of the combustion chamber liner connects to the upstream end of the transition duct. The combustor liner isolates the extreme temperature, flame, and byproducts produced by the combustion process, and directs the resulting hot working gas into the turbine section of the engine via the transition duct.
It is important to keep the temperature of the combustor liner within design limits while using minimum cooling air. The cooling air comes from the compressor of the engine. Any air diverted for engine cooling reduces the air available for combustion. Therefore, the less compressed air that is diverted, the more efficient is the engine. Also, the less compressed air that is used for film cooling of the combustor liner the less the working gas is diluted, which also improves engine efficiency. However, exceeding the temperature limits of the combustor liner can produce thermal coating spallation, base metal oxidation, and undesirable hot gas flow path deformation, so highly effective cooling is needed.